Well, it's finally happened: we've discovered more of Deinocheirus.
That's the giant pair of arms dug up from Mongolia nearly fifty years ago -
Aside from a few ribs and vertebrae at the same site, no other evidence of it had been discovered during all that time, so it's been rather mysterious. The arms have been attributed to all kinds of creatures over the years, but for the last decade or two the consensus has been that they were attached to a gargantuan ornithomimosaur, the same family as Gallimimus.
Well, the discovery's just been announced of two new, nearly complete skeletons. Apparently the consensus was fairly accurate - it's an ornithomimosaur, though a survivor from a more basal family line than the ones we see the most of in pop culture.
And
huge - 11 metres long, 5 metres tall. Unfortunately we're still missing their skulls, but there's one really weird and unexpected feature: they had some form of sail or hump above their pelvis, indicated by the presence of tall neural spines on the vertebrae. We don't see evidence of this in any other coelurosaur, so even disregarding the fact that it's vastly larger than any of its close relatives, it's a very unique animal.
The three images present appearances for whether it was scaly, partially or wholly feathered. Given its giantism, it wouldn't have needed much in the way of insulation, so I'd imagine it'd be somewhere between the first two.
More info:
http://news.nationalgeographic.com/news/2013/11/131104-dinosaur-hands-arms-body-mongolia/http://chasmosaurs.blogspot.co.uk/2013/11/svp-dispatches-body-of-deinocheirus.html